[c-nsp] problem of both "ip route 0.0.0.0" and "ip default-gateway" configured

[Paul Stewart]

We've ran across both before when a layer3 switch is involved that was
previously used for layer2 functions only - worked fine, but we did go back
and remove the "ip default-gateway" statement...

Paul


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jon Lewis
Sent: Saturday, January 12, 2008 11:25 AM
To: sthaug at nethelp.no
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] problem of both "ip route 0.0.0.0" and "ip
default-gateway" configured

On Sat, 12 Jan 2008 sthaug at nethelp.no wrote:

>> Someone mentioned that configuring both commands on the same
router/switch
>> causes trouble, i wonder if someone can help me understand why?
>>
>> 1) ip route 0.0.0.0 next-hop
>> 2) ip default-gateway next-hop
>
> Why do you *want* to configure both? 1 is supposed to be used for an L3
> box (router), 2 is supposed to be used for an L2 box (switch).

AFAIK, ip default-gateway is only used when IP routing is off/unsupported. 
It can be useful if a device ends up booting into boot IOS that doesn't 
support routing (like some of the older run from flash platforms during a 
software upgrade where you have to reboot from ROM, download new code to 
flash, and then boot the new code).  I've got lots of gear with both a 
default route and an ip default-gateway and no problems.

> If the interface in question is a broadcast medium (Ethernet), the router
> doesn't know the next-hop address, resulting in a high rate of ARPs. This
> has been dicussed on the list many times before, and the advice is simple:
> Don't do it!

It can work...but its very delicate and really pisses people off when 
someone with more clue is asked to take over management of the network.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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